This invention relates to modulated circuits. In particular it relates to laser modulators of laser diodes; and, even more specifically it relates to laser modulators of laser diodes capable of providing high current, fast rise time, narrow pulses.
Previous circuits that were used to provide these results were limited by the fact that with the use of silicon controlled rectifiers, SCRs, the fastest SCRs available had low breakdown voltages. To increase the peak pulse current of such a circuit without increasing the rise time or pulse width required increasing the supply voltage. However, supply voltage could not be increased beyond the breakdown voltage of the SCR. Alternate circuits which could avoid the difficulty of breakdown voltage ran into the problem that by using multiple SCRs the turn on time was limited by the turn on time of the slower SCR. The overall turn on time and rise time were slower than single SCR circuits which had breakdown voltage limitations.
The need for high current is so the laser diode is able to provide a stronger signal. The need for narrow pulses is to prevent over heating. The requirement for fast rise time is to allow electronic range gating by use of a laser diode. Without a fast rise time it is impossible to use laser diodes for electronic ranging of targets. Electronic ranging as used here refers to using the time of return of the leading edge of a pulse from a target to determine the range to the target, as in radar systems.